Adjustable curve ruler



April 3, 1934. w. s. WESTON ADJUSTABLE CURVE RULE Filed Aug. 5, 1932 3 Sheets-Sheet -l Inventor W/H/am 6. W66 70/7 0 ck vTmnur -22 1 I I L April 3, 1934. w. s. WESTON ADJUSTABLE CURVE RULER Filed Aug. 5, 1932 3 Sheets-Sheet 2 flags.

T T I I l N l o0 Inventor 7 E Wf/l/am 5. W66 20/1 x /444, Wx/ZWK "W April 3, 1934. w. s. WESTON 1,953,283

ADJUSTABLE CURVE RULER Filed Aug. 5, 1932 a Sheets- Sheet 5 Inventor:-

Patented Apr. 3, 1934 D STAES 4 Claims.

The invention relates to an adjustable ruler for the use of draftsmen and others in the drawing and checking of curves. It comprises a flexible arc member of constant or invariable length;

rigid end members attached in fixed relation to the ends of the arc member and providing edges that are tangent to the curve of the arc memher at the ends thereof; and a rigid member intermediate the end members on which the end members are mounted in an adjustable rotative relation that is utilized in the process of flexing and holding the arc member to any desired curvature. My present invention is an improvement on the curve ruler disclosed in my Patent No. 1,893,689, issued January 10, 1933, utilizing in the construction the fundamental principle disclosed in that patent, and providing an instrument that may be adjusted for the ruling of an arc of a circle, or for the ruling of an ir- ZOregular curve. The invention is hereinafter more fully described, illustrated in its preferred embodiment in the accompanying drawings, and more particularly pointed out in the appended claims.

Referring to the drawings:--

Fig. l is a plan view of the improved curve ruler with the arc member in the straight line position; that is, the position for a radius of infinite length.

Fig. 2 is an elevation of the instrument in the straight line position of Figure 1 showing the uniform thickness of the main parts, permitting its use either side up, particularly for irregular curves.

Fig. 3 is a-plan view with the end members each rotated through an angle of '75 degrees in a manner to uniformly flex the arc member and provide an arc of a circle covering an angle of 150 degrees.

Fig. 4 is a detail plan view of the upper end of Figure 3, with a cover plate removed, showing the clamping device used in holding the end members to the correct angles for the desired curve.

Fig. 5 is a diagram showing the relative location of the fundamental points utilized in and governing the construction of the instrument.

Figs. 6 and 7 are plan views each showing the end members adjusted to different angles, there- 50 by developing a non-uniform strain in the are member and causing it to take the shape of an irregular curve.

The are member A is made of a ribbon of spring steel or other highly resilient material having a 55 uniform elastic quality throughout its length.

The ends of the ribbon are attached to end members F and F preferably by welding or soldering so that only that portion of the ribbon between the end members, constituting the arc member, is flexed when the end members are '60" moved rotatively toward each other. The points where the ribbon clears the end members are therefore the ends of the arc, and in accordance with the common practice of engineers and draftsmen, are designated as PC, point of curve, and PT, point of tangent, the terms being interchangeable and used to distinguish one end of a curve from the other. The ends of the ribbon attached to the end members constitute tangents to the curve of the arc portion and by common practice are designated by the letter T. The end members F and F are rctatively mounted in the ends of an intermediate and main holding frame B in a manner such that, when symmetrically rotated through equal angles to a position like that of Figure 3, the direct or chord distance between the PC and PT ends and the relative angle of the tangents are correct for the arc member of invariable length flexed to the arc of a circle. For this position the uniform resilient quality of the ribbon can be depended upon, in absence of external pressure, to hold the uniformity of the arc to that of a circle sufficiently close for all practical uses as a drafting instrument.

New and improved means for operating and controlling the rotative movement of the end members together with points on the frame B providing intermediate bearings for the concave side of the arc member when curved to the arc of circles constitute the present invention. The construction is based on the fundamental fact that when the arc member of invariablelength is flexed to the arcs of circles there are points in fixed relation to one end 'member that are paired with and remain at a substantially constant distance from points in fixed relation to the other end member, as disclosed in the patent referred to. In that patent for any pair of points used the sum of the angles of rotation of the end members, relative to a straight line connecting the points, is equal to the change in the curvature of the arc member. In the present construction only one pair of points are utilized. The points chosen, indicated by the letters 0 and 0 lie in extensions of the tangent lines of the end members, at a constant distance from the PC and PT ends respectively. Only with the points 0 and 0 located symmetrically on the tangent extensions are the angles of rotation of of 150 degrees each member is rotated 75 de- Figure 4, consists of an eccentric disc at with a the end members, relative to the straight line between the points, each equal to half the angle of curvature of an arc of a circle of constant length. Referring to Figures 1 and 3, for an are 7.854 inches long point 0 is 1.377 inches from PC end and point C) is the same distance from the PT end. For arcs of circles covering angles from zero, the straight line position of Figure 1, up to 150 degrees, the position of Figure 3 with a radius of 3.0 inches, the distance between points 0 and O is 5.1 inches.

The new and improved means for operating and controlling the rotative movement of the end members is embodied in the construction illustrated whereby the end members F and F are rotated at constant distance from and around points 0 and 0 respectively, without a mate-' rial connection with these points. Point 0 may be called the rotative center for member F and point 0 the rotative center for member F The end members are each provided with a curved armG andG 'respectively, mounted in a curved groove in the adjacent end of the frame B and concentric with their rotative centers. The rotativemovei'nent of the end member is accomplished by sliding the curved arm through the ture of the arc member.

For arcs of circles the end members are each rotated through the same angle from the straight line position, following the scale worked on the curved arms. As shown in Figure 3, for an arc gr'ees. With an are 7.854 inches long the total angle to be covered for any particular radius is determined by dividing 450 by the radius in inches. In Figure 3, the radius in proportion to the other dimensions is 3.0, and the angle 150 bers have been rotated the correct amount for the curvature desired by sliding the curved arms through the curved grooves of the main frame B, it is necessary to clamp the arms against further movement. A preferable means, as illusrated in lever arm 0 pivotally mounted in the frame and a fold h'of' spring steel interposed between the disc and the edge of the curved arm. The curved arm is clamped by simply rotating the disc (1 by means of the lever c in a manner to compress the folded spring and hold the arm in high pressure contact against the opposite side of the groove. The friction due to this pressure will be sumcient underlordinary conditions to prevent the curved arm from sliding out of adjustment. The groove and the'pocket holding the disc d and spring h is midway between the top and bottom of the frame B} as shown in Figure 2. To facilitate this construction, the top portion is made of a separate plate I) held in place by screws. The plate I) is removed in Figure 4. The clamping mechanism at the'two ends of the frame B are duplicates' except arranged right and left. I

To preventthe curved arms G and G from being pulled out of this circular groove by a movement the reverseo-f that produced'in Figure 3, the ends are provided with shoulders s. The curved arms are preferably madelong enough to come in contact with the concave'sides of thearc member when adjustable to the minimum radius for which the instrument is constructed, as shown in Figure 3.

Referring to the diagram of Figure 5, the length of the are for arc curvatures between the straight line position with an infinite radius and that covering an angle of 150 degrees, with a radius of 3.0 is 7.854. The curves shown have their centers located and so spaced on a line bisecting the curves that the curves all intersect the line of the straight line position at point I and I which are 4.31 apart and 1.772 distant respectively from the straight line ends. For this relative location of the curves all tangents to the ends intersect the line of the straight line position substantially at the same point, tangents to the PC end intersecting at point 0 and tangents to the PT end intersecting at point 0 The distance between each of these points and the adjacent straight line end of the arc member and the adjacent curve ends is 1.377, correct to a fraction in the third decimal place for all arcs of circles between the straight line and the curve covering 150 degrees. For an arc 7.854 in terms of inches the variation is less than one hundredth of an inch, and immaterial in the construction of the instrument.

As heretofore described, the points 0 and O constituting the rotative centers for the end members F and F are in fixed relation to the main frame B in'which the end members are rotativel y mounted. Points I and I in the straight line through points 0 and O at fixed distances are also in fixed relation to the main frame B. I: take advantage of this fact and provide the frame with arms J and J 2 extended to the points I and 1 respectively and so shaped as to provide a bearing for the arc member A at those points when the member is curved to the-arc of any circles between the straight line position and the arc of 150 degrees. Points 1 and I of the main frame thus constitute supports for the concave side of the arc member intermediate its ends when curved to arcs of circles. It may be noted that points 0 0 I andl are theoretically figured for the center line of the ribbon constituting thearc member. Allowance for half the thickness of the ribbon istherefore made in the finish of the arms J and J 2 at the points and'the adjacent edges. This detail is indicated in Figure 4.

Referring now to Figures16 and 7, it will be noted that with separate and independent adjusting mechanism the end'members can be rotated through different angles and held to any desiredrelation; In Figure 6 the right hand member only is rotated, lifting the flexible arc member by, the bending strain at that end above the straight line position held at the left hand end, and resulting in a reverse curve. By rotating the left hand member from the position of Figure 6 tothat shown in Figure 7 the reverse curve is changed to an easement curve like a spiral with the curvature gradually decreasing from one end to the other. By adjusting the end members to different angles, the draftsman may obtain an irregular curve suitable to his purpose. Any irregular curve can be reproduced by making a, record of the anglesof adjustment of the'two end members. For irregular curves, only one of the points I and 1 carriedby the mainframe provides a bearingfor the arcmember, the point at the short radius end of the arc.

Thelength of the arc member A, which is constant for all angles of curvature, is necessarily measured along the center line of the ribbon forming the member. In the manufacture of the instrument, after the length of the arc member has been decided upon, the location of the rotation centers and the other dimensions will be in proportion to those given in these specifications. From the length of the arc member and the total angle of the equal adjustment of the end members for any circular curve the radius may be determined by trigonometry. With an arc 7.854 inches long the total angle is equal to 450 divided by the radius, as previously stated. If the length is changed, then the number 450 is to be changed in the same proportion.

I claim as my invention:-

1. An adjustable curve ruler for arcs of circles comprising a flexible arc member of constant length, rotative end members rigidly attached to the ends of the arc member, means whereby the center of rotation of each end member is located on a line which is tangent to the end of the arc member in each or" its positions, and at a constant distance from said end, a rigid intermediate frame spacing saidrotative endmembers andsaid means in a manner whereby the said centers of rotation are held at a constant distance apart, and means for holding the end members against further rotation when adjusted to the desired position.

2. An adjustable curve ruler comprising a flexible arc member of constant length, end members *igidly attached to the ends of the arc member and rotatable in the process of flexing the arc member to any desired curvature, a rigid intermediate frame supporting the end members, two fixed points on the intermediate frame adapted to bear against the concave side of the arc member when flexed to the arc of a circle, and means for holding the end members against further rotation when adjusted for the desired curvature.

3. An adjustable curve ruler for arcs of circles comprising a flexible arc member of constant length, end members rigidly attached to the ends of the arc member, each providing an edge that is tangent to the arc member and each having a curved arm, a rigid intermediate frame between the end members, having a groove in each end .in which the curved arm of the adjacent end member has a slidable movement whereby rotative movement is imparted to the respective end members and whereby the centers of rotation of the end members are held at a constant distance apart, and means for holding said curved arms in said grooves when moved to any desired angle of rotation.

4. An adjustable curve ruler for arcs of circles comprising a flexible arc member of constant length, end members rigidly attached to the ends of the arc member and adapted to be rotatively moved toward each other in the process of flexing the arc member from the straight line position to an arc of a circle, and means adjustably connecting the end members wherein a single if;

center of rotation for each end member is utilized in the construction, said centers being held at a constant distance apart and each being located on an extension of the tangent to the are at the attached end, and whereby when both end members are rotated toward each other through equal angles from the straight line position of the arc member the ends of the arc member are moved and held in correct relation for an arc of a circle with a curvature equal to the sum of the said two equal angles of rotation.

ILLIAM S. WESTON. 

